Aircraft control system including limiting means

ABSTRACT

A feedback system for controlling an aircraft as a function of a primary flight parameter and including limiting means whereby a secondary flight parameter becomes the controlling feedback parameter.

0 United States Patent 1 3, 3 Pfersch 51 Apr. 25, 1972 [54] AIRCRAFTCONTROL SYSTEM 3,242,407 3/1966 Hansen ..318/619 INCLUDING LIMITINGMEANS 3,241,792 3/1966 Hattendorf ..318/584 3,424,402 1/1969 Bulloch eta1... ..3l8/635 [72] Inventor: George H. Pfersch, Randolph Township,

Moms County Primary Examiner-l-larold Broome [73] Assignee: The BendixCorporation Attorney-Anthony F. Cuoco and Plante, Hartz, Smith and 22Filed: June19, 1970 [21] App1.No.: 47,850 [57] ABSTRACT A feedbacksystem for controlling an aircraft as a function of a :ttSbCll primaryflight parameter and including limiting means [58] Fieid "'318/584 561619 wherebyasecondary flight parameter becomes the controlling feedbackparameter. [56] References Cited 7 Claims, 1 Drawing Figure UNITEDSTATES PATENTS 3,241,027 3/1966 Albright ..3l8/561 2 4 IO 22 a4CgP'lfQND SERVO W DEVICE SYSTEM I I 1 I4 l I l PIT I I GYRO l I I 16 lNORMAL 6 ACCEL. L g l x ANGLE OF ATTACK SENSOR AIRCRAFT CONTROL SYSTEMINCLUDING LIMITING MEANS BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to feedback control systems of the typefor controlling aircraft and, more particularly, to limiting means forsaid systems.

2. Description of the Prior Art Aircraft control systems include meansfor providing a signal corresponding to a commanded value of a flightparameter and sensing means mounted to the craft for providing a signalcorresponding to the actual value of the parameter. The actual parametersignal is fed back and summed with the command signal for providing acontrol signal.

Often, especially when controlling modern high speed craft, thecontrolled parameter affects some secondary parameter and limiting isrequired to prevent the secondary parameter from reaching a criticalvalue.

SUMMARY OF THE INVENTION This invention contemplates an aircraft controlsystem including sensors for providing signals corresponding to primaryand secondary flight conditions and a signal source for providing asignal corresponding to a commanded value of the primary flightcondition. The secondary flight condition signal and the command signalare combined and limited and the primary flight condition signal iscombined in feedback relation with the limited signal to close a controlloop for providing a control signal, The signal combinations are suchthat when the secondary flight condition signal is less than apredetermined limit it has no effect on the control loop and when thelimit is equalled or exceeded the limited signal is a command for a newcontrol loop with the secondary flight condition being the feedbackfunction.

One object of this invention is to control an aircraft fora primaryflight condition and to limit the control as a function of a secondaryflight condition affected by the primary flight condition.

Another object of this invention is to limit the effect that variationsin the primary flight condition have on the secondary flight condition.

Another object of this invention is to provide a control system whichaffects control as a function of a primary flight condition. A primaryflight condition command signal is com bined with a sensed secondaryflight condition signal and the combined signal is applied to a limiter.When the combined signal is below the limit of the limiter the secondarycondition signal has no effect on the control channel, but when thecombined signal equals or exceeds the limit the combined signal is acommand for a control loop with the secondary signal being the feedbackparameter.

The foregoing and other objects and advantages of the invention willappear more fully hereinafter from a consideration of the detaileddescription which follows, taken together with the accompanying drawingwherein one embodiment of the invention is illustrated by way ofexample. It is to be expressly understood, however, that the drawing isfor illustration purposes only and is not to be construed as definingthe limits of the invention.

DESCRIPTION OF THE DRAWINGS The single FIGURE of the drawing is a blockdiagram of an aircraft control system according to the invention.

DESCRIPTION OF THE INVENTION When controlling vertical flight of anaircraft critical parameters include pitch rate, normal acceleration andangle of attack. Pitch rate and normal acceleration are sensed andsignals corresponding to the sensed parameters are added. The additionsignal and a signal corresponding to a commanded value of pitch rateplus normal acceleration are compared and the craft is controlled by aservo system in response to the difference signal.

Angle of attack may be defined as the angle formed by the chord of thewing of the craft and the direction of the air through which the wingmoves. For any wing section there is an angle of attack which creates amaximum lift (the upward force that opposes the pull of gravity on thecraft). If this angle of attack is exceeded, the lift will decrease andthe craft will stall.

In order to preclude the above-mentioned stalling it is necessary thatthe aircraft be flown at a pitch attitude that will maintain properangle of attack. Therefore, when controlling the vertical flight of thecraft in response to pitch rate and normal acceleration signals, forexample, the control signal derived from said signals must be limited asa function of angle of attack.

In accordance with the above, an aircraft control system according tothe invention and as shown in the drawing includes a signal source 2 forproviding a signal C corresponding to commanded pitch rate plus normalacceleration of an aircraft 8. Signal C* is applied to a summing means 4and summed thereby with a signal a corresponding to angle of attack ofaircraft 8 and provided by a sensor mounted to the aircraft. The signalfrom summing means 4 is applied to a limiter 10 which limits the signalas will be hereinafter described and the limited signal is applied tosumming means 12 and summed thereby with angle of attack signal a.Limiter 10 is a conventional type device and may be of the typedescribed at pages 412-414, Electronics for Scientists, Malmstadt, etal., W.A. Benjamin, Inc., New York, 1963, and is connected to summingmeans 4 as will be understood by those skilled in the art.

A pitch rate gyro 14 mounted to aircraft 8 provides a pitch rate signal(i and a normal accelerometer 16 mounted to the craft provides a normalacceleration signal A Signals 0 and A are added by a summing means 18which provides a signal C* corresponding to actual pitch rate plusnormal acceleration of aircraft 8.

The signal from summation means 12 and signal C* from summation means 18are subtracted by a summation means 20 and the difference signaltherefrom is applied to an amplifier 22 having a predetermined gain Kfor providing a control signal 8. Control signal 5 is applied to a servosystem 24 which is coupled by suitable mechanical means as will beunderstood by those skilled in the art to a control surface (elevator)of aircraft 8 for operating the control surface.

Servo system 24 is a conventional device of the type including a servoamplifier, a servo motor for driving a rate generator and appropriatefollow-up means such as described in US. Pat. No. 2,879,015 to Ardia andassigned to the Bendix Corporation, assignee of the present invention.

Summing means 4, 12, 18 and 20 may be conventional devices of theoperational amplifier type such as described at page 354, Electronicsfor Scientists, supra, and likewise connected as will be understood bythose skilled in the art.

OPERATION In the context of the invention, pitch rate plus normalacceleration is a primary flight parameter and angle of attack is asecondary parameter for which limiting is required. Angle of attacksignal a is applied to the control signal chain at summing means 4 whereit is added to command signal C. The signal from summing means 4 islimited by limiter 10 and the limited signal and angle of attack signala are subtracted by summing means 12.

When angle of attack signal a is less than a predetermined limitestablished by limiter 10, its contribution to the control signal chainis zero because of the unity addition and subtraction of the signalbefore and after limiting, respectively. However, when the sum ofcommand signal 6* and angle of attack signal 0: equals or exceeds thepredetermined limit, the output of limiter 10 is in effect a commandsignal for a new control loop with angle of attack being the feedbackparameter. Since the command to this loop is constant, the feedbackparameter attempts to remain constant within its loop responsecapabilities. Thus, the secondary parameter, angle of attack, is limitedas long as the input signal to the limiter remains at or above thepredetermined limit.

Although but a single embodiment of the invention has been illustratedand described in detail, it is to be expressly understood that theinvention is not limited thereto. Various changes may also be made inthe design and arrangement of the parts without departing from thespirit and scope of the invention as the same will now be understood bythose skilled in the art.

What is claimed is:

l. A control system comprising:

first sensing means for providing a signal corresponding to a primarycondition;

a signal source for providing a primary condition command signal;

second sensing means for providing a signal corresponding to a secondarycondition;

means connected to the signal source and to the second sensing means forcombining the command signal and the secondary condition signal;

means connected to the combining means for limiting the combined signal;

means connected to the limiter and to the second sensing means forcombining the limited signal and the secondary condition signal;

means connected to the last mentioned combining means and to the firstmentioned sensing means for combining the signals therefrom and forproviding a control signal; and

means responsive to the control signal for affecting control.

2. An aircraft control system comprising:

means for providing a pitch rate signal;

means for providing a normal acceleration signal;

means for providing an angle of attack signal;

means for providing a signal corresponding to a commanded sum of pitchrate and normal acceleration; means for adding the angle of attacksignal and the command signal;

a limiter connected to the adding means for limiting the signaltherefrom;

means connected to the angle of attack signal means and to the limiterfor subtracting the signals therefrom;

means connected to the pitch rate signal means and to the normalacceleration signal means for adding the signals therefrom;

means connected to the subtracting means and to the last mentionedadding means for subtracting the signals therefrom and for providing acontrol signal; and

means connected to the control signal means and to the aircraft forcontrolling the craft in response to the control signal.

3. A control system as described by claim 1 wherein the system controlsan aircraft and the means for providing a signal corresponding to aprimary condition includes:

means for providing a signal corresponding to the pitch rate of thecraft;

means for providing a signal corresponding to the normal acceleration ofthe craft; and

means connected to the pitch rate signal means and to the normalacceleration signal means for adding the signals therefrom.

4. A control system as described by claim 3, wherein:

the means for providing a signal corresponding to a secondary conditionincludes means for providing an angle of attack signal.

5. A system as described by claim 4 wherein the means connected to theprimary condition command signal means and the secondary conditionsignal means for combining the signals therefrom includes:

means connected to the command signal means and means connected to theangle of attack signal means for adding the signals therefrom.

6. A control system as described by claim 5 wherein the means connectedto the limiter and to the secondary condition signal means for combiningthe signals therefrom includes:

means connected to the limiter and to the angle of attack signal meansfor subtracting the signals therefrom.

7. A control system as described by claim 6 wherein the means connectedto the last mentioned means and to the primary condition signal meansfor combining the signals therefrom and for providing a control signalincludes:

means connected to the means for subtracting the limited signal and theangle of attack signal and connected to the means for adding the pitchrate signal and the normal acceleration signal for subtracting thesignals from said subtracting and adding means.

1. A control system comprising: first sensing means for providing asignal corresponding to a primary condition; a signal source forproviding a primary condition command signal; second sensing means forproviding a signal corresponding to a secondary condition; meansconnected to the signal source and to the second sensing means forcombining the command signal and the secondary condition signal; meansconnected to the combining means for limiting the combined signal; meansconnected to the limiter and to the second sensing means for combiningthe limited signal and the secondary condition signal; means connectedto the last mentioned combining means and to the first mentioned sensingmeans for combining the signals therefrom and for providing a controlsignal; and means responsive to the control signal for affectingcontrol.
 2. An aircraft control system comprising: means for providing apitch rate signal; means for providing a normal acceleration signal;means for providing an angle of attack signal; means for providing asignal corresponding to a commanded sum of pitch rate and normalacceleration; means for adding the angle of attack signal and thecommand signal; a limiter connected to the adding means for limiting thesignal therefrom; means connected to the angle of attack signal meansand to the limiter for subtracting the signals therefrom; meansconnected to the pitch rate signal means and to the normal accelerationsignal means for adding the signals therefrom; means connected to thesubtracting means and to the last mentioned adding means for subtractingthe signals therefrom and for providing a control signal; and meansconnected to the control signal means and to the aircraft forcontrolling the craft in response to the control signal.
 3. A controlsystem as described by claim 1 wherein the system controls an aircraftand the means for providing a signal corresponding to a primarycondition includes: means for providing a signal corresponding to thepitch rate of the craft; means for providing a signal corresponding tothe normal acceleration of the craft; and means connected to the pitchrate signal means and to the normal acceleration signal means for addingthe signals therefrom.
 4. A control system as described by claim 3,wherein: the means for providing a signal corresponding to a secondarycondition includes means for providing an angle of attack signal.
 5. Asystem as described by claim 4 wherein the means connected to theprimary condition command signal means and the secondary conditionsignal means for combining the signals therefrom includes: meansconnected to the command signal means and means connected to the angleof attack signal means for adding the signals therefrom.
 6. A controlsystem as described by claim 5 wherein the means connected to thelimiter and to the secondary condition signal means for combining thesignals therefrom includes: means connected to the limiter and to theangle of attack signal means for subtracting the signals therefrom.
 7. Acontrol system as described by claim 6 wherein the means connected tothe last mentioned means and to the primary condition signal means forcombining the signals therefrom and for providing a control signalincludes: means connected to the means for subtracting the limitedsignal and the angle of attack signal and connected to the means foradding the pitch rate signal and the normal acceleration signal forsubtracting the signals from said subtracting and adding means.